The present invention relates to a pneumatic tire, more particularly to a tread pattern suitable for a winter tire and capable of improving running performance on snowy roads and running performance on icy roads in a good balance.
Winter tires or pneumatic tires for the winter season are required to have running performance on snowy roads (hereinafter, snow performance) and running performance on icy roads (hereinafter, ice performance) which are improved in a good balance at high levels.
For instance, in order to improve ice performance by increasing the ground contacting area of the tread, if the widths of tread grooves are decreased, then, during running on snowy roads, shearing force of snow packed into the tread grooves is decreased, and snow performance is deteriorated. Thus, it is difficult to improve snow performance and icy performance in a good balance at high levels.
Japanese Patent Application Publication No. JP-A-2009-269500, directed to improve snow performance and icy performance of a pneumatic tire in a good balance, teaches to specifically define the widths of five land zones which are axially divided by four circumferentially-continuously-extending main grooves, to form each land zone as a row of blocks, and to provide a circumferentially-continuously-extending narrow groove for each of the middle land zones. However, there is room for improvement on such pneumatic tire.